Advisory ids must be last path segment in URL

Instead of the title, advisory ids should be used as path segment in URL

Ideally the url should look like this:

https://typo3.org/security/advisories/typo3-ext-sa-2017-019/ or https://typo3.org/security/advisories/typo3-core-sa-2017-007/

Redirects from old URLs should be applied